Rapid escalation of chemical feedstock costs in recent years has spurred efforts to utilize sources which were previously considered uneconomic. One result of such efforts is the development of processes for the cracking of heavier crude oil fractions in order to produce ethylene and other chemical feedstocks.
One difficulty inherent in the utilization of such fractions is that they are so hydrogen deficient that the yield of valued materials is lower and the capital and operating costs are increased. On the other hand, in general, heavier and higher sulfur feedstocks have a decreasing range of end uses and are valued accordingly. Thus, such feedstocks appear to be singularly economically attractive. One process, that described in U.S. Pat. No. 2,527,575, utilizes heavy feedstocks in a multistage process, the method being characterized by severe heat treatment to coke the feedstock and produce, inter alia, some normally gaseous hydrocarbons. However, the apparent severity of the coking procedure described would limit the volume of gaseous hydrocarbons produced. Accordingly, a cracking process which capitalized on the low cost of heavy feedstock materials, overcame the environmental and disposal problems associated with the residual products, and which produced good yields of light olefins and other useful products could have great economic importance. The present invention is such a process.